Method and system for extraction of oil from corn

ABSTRACT

A process for removing oil from an agricultural substrate, including a dry grind corn. An ethanol solution with a concentration in the range of from about 90% to about 100% ethanol is mixed with the dry grind corn in a ratio of from about 10:1 to about 1:1 to form an extraction solution including the ethanol solution, oil, and corn solids. The extraction solution is separated into the corn solids and a filtrate, the filtrate including the ethanol solution and oil. The filtrate is membrane filtered, including nanofiltration, to restrain an oil concentrate from the filtrate and pass a permeate of the ethanol solution. The oil contained within the oil concentrate is purified.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 10/913,790,filed Aug. 6, 2004, now U.S. Pat. No. 7,045,607, which is acontinuation-in-part of U.S. application Ser. No. 10/190,365, filed Jul.3, 2002, now abandoned which is a continuation of U.S. application Ser.No. 09/313,690, filed May 18, 1999, now U.S. Pat. No. 6,433,146, issuedAug. 13, 2002.

FIELD OF THE INVENTION

The present invention generally concerns corn milling processes andmachines.

BACKGROUND OF THE INVENTION

There are two primary types of corn processing conducted presently: drygrind and wet milling processes. The wet milling processes are efficientin their use of corn since they produce numerous high value cornproducts, such as corn oil, starch, corn gluten meal, corn gluten feed,and corn steep liquor. However, the wet milling processes require veryhigh capital investments in machinery. Dry grind processes are used toproduce ethanol and animal feed. Animal feed is substantially lessvaluable than corn oil and zein, which are left in the animal feedproduced by a dry mill process. A reason for existence of the dry grindplants to date has been government ethanol subsidies, which are likelyto disappear.

Some methods to extract oil and zein from dry mill corn have beenproposed in the literature, but have yet to demonstrate efficiencymeeting commercial production requirements. One type of proposed methodis embodied in U.S. Pat. No. 4,716,218 and a “Sequential ExtractionProcess” developed at Iowa State University. This type of method usesethanol to extract oil and zein. Evaporation is required to remove theethanol, and then hexane-extraction is used to separate the oil from thezein with further subsequent evaporation of the hexane from the oil.These are relatively complicated processes. They are also expensive dueto their energy intensive nature. Significant heating requirementsresult from the multiple required evaporations. Further, theevaporations create pollution concerns.

Another proposed method to remove oil from dry-milled corn is mechanicaldegermination. This method produces corn germ with less thanapproximately 50 percent oil. The germ must be subsequently processed torecover the oil. No ability to recover zein is presented by this method,however, and there is no known utilization of the method to obtain cornoil and zein in a manufacture scaled product.

Thus, there is a need for an improved method capable of using dry grindcorn, as well as wet milled corn product, to produce one or more cornproducts of value. It is an object of the invention to provide such amethod. It is a further object of the invention to provide a method forextracting corn oil and/or protein (particularly zein), which method iscapable of utilizing dry grind corn or wet milled corn product throughethanol treatment with filtration.

SUMMARY OF THE INVENTION

The method of the present invention obtains oil from various forms ofcorn to meet or exceed such needs. Membranes are relied upon to filterthe oil and/or zein. Input to the corn process of the invention is cornof multiple forms. Ethanol is the only reagent utilized by the process,and conventional dry and wet mill plants therefore already provide thenecessary reagent supply for implementation of the invention, thoughethanol from any source may be used.

The invention may serve as the basis for an add-on technology to anexisting dry mill or wet mill plant, as well as the basis upon which newdry mill and wet plants may be constructed. Dry mill plants are likelyto benefit significantly from preferred embodiments of the invention,since the invention provides ways to extract more valuable oil and/orzein from the corn while making use of the basic dry mill equipment andproducts of conventional dry mill plants.

A plant modified or constructed to implement a preferred process of theinvention may use high concentration ethanol, approximately 90–100%ethanol, to separate oil from the corn. The corn may be in any form,e.g., wet mill product, dry flakes, dry particles, or whole kernels.Membrane filtration may be used to concentrate the oil and/or zein, andto recover the ethanol for further use in processing, if desired.Recycled ethanol may then be used in additional extraction of oil and/orzein, or may be used in a distillation operation if ethanol product isalso being produced by the plant.

Generally, in a process for removing oil from an agricultural substrate,including a dry grind corn, an ethanol solution with a concentration inthe range of from about 90% to about 100% ethanol is mixed with the drygrind corn in a ratio of from about 10:1 to about 1:1 to form anextraction solution including the ethanol solution, oil, and cornsolids. The extraction solution is separated into the corn solids and afiltrate, the filtrate including the ethanol solution and oil. Thefiltrate is membrane filtered, including nanofiltration, to restrain anoil concentrate from the filtrate and pass a permeate of the ethanolsolution. The oil contained within the oil concentrate is purified.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, objects, and advantages of the invention will beapparent to those skilled in the art from the following detaileddescription and by reference to the drawings, of which:

FIG. 1 illustrates corn oil production according to principles of thepresent invention;

FIG. 2 illustrates zein production according to principles of thepresent invention; and

FIG. 3 illustrates combined oil and zein production according topreferred embodiments and methods of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention extracts oil and/or zein from corn or corn processingby-products using ethanol, and relies upon membrane filtration to obtainhigh value oil and/or zein concentrate. The extraction is done in acontinuous countercurrent, co-current or mixed flow extraction system.The sole reagent relied upon by the process is ethanol, which may berecycled for additional extraction or may be used to produce ethanolproduct.

Referring now to FIG. 1, shown is a flow diagram of an oil concentrateextraction application of the invention to a dry mill ethanol plant.Corn or corn processing by-products are input to a dry grind processingstep 10. The corn may be, for example, whole kernel or flaked corn. Ifcorn processing by-products such as DDG or DDGS (distiller dried grains,with solubles), corn gluten meal, corn germ, or corn meal are used, thisstep 10 may not be necessary. In all cases, moisture content of feedmaterial should be 0–14% by weight. The corn and ethanol are mixed instep 16 for extraction of oil. The temperature of extracting should be50–90° C., preferably close to the boiling point of ethanol (78° C.) if100% ethanol is used. The time of extraction should be 10–120 minutes,preferably 30 minutes if a batch extraction is done.

The mixing step prepares the corn for a preliminary extraction step 16.Small processing plants might use batch extraction, and larger plantscould use continuous-counter current extraction. Oil extraction usesethanol of between approximately 90–100% concentration, however, it isnoted that oil extraction at around 90% ethanol is highly inefficient,and at least a 95% concentration is preferred. The ethanol is preferablysupplied by the plant conducting the process of the invention, and,since it may be one of the corn products produced by application of thepresent process, a self sustaining supply is provided by the plant. Noother reagent is required.

A separation step 18, e.g., filtration or centrifugation, is conductedto remove corn solids from an ethanol, zein, and oil mixture produced bythe extraction step 16. The objective of the separation step is toremove substantially all suspended corn solids from the dissolved cornmixture of ethanol, oil, and small portions of the ethanol-solubleprotein zein. Some zein will not be extracted from the corn solids. Ifzein is the primary objective, the ethanol concentration may be adjustedwithin the aforementioned 60–90% range to optimize zein extraction.Generally, ethanol concentrations in the higher end of the range willextract less zein than ethanol concentrations in the lower end of therange.

The separated corn solids from step 18 are subjected to a desolventizingstep 19 to remove any ethanol that may be adsorbed in the corn solids.The ethanol recovered from desolventizing step 19 is recycled to thedistillation section of the plant. The desolventized corn solids providethe necessary input for conventional ethanol production according toconventional techniques. Thus, in a plant embodying preferred methodsand systems of the invention, fermentation and distillation steps 20 and22 are preferably conducted to produce an ethanol supply for theextraction step 16. Fuel ethanol and distillers dried grains withsolubles (DDGS—an animal feed) may also be output as product from aplant modified or constructed to implement the invention.

The filtrate from step 18 containing oil, ethanol, and co-extractedcomponents such as zein is then processed in a nanofiltration step 24using a membrane to restrain oil while allowing ethanol to pass through.Corn oil has a molecular weight of about 800–900 daltons. Selection ofan appropriate membrane is therefore straightforward. Nanofiltrationmembranes that are stable in ethanol, such as those made by KochMembrane Systems, Osmonics-Desal or USFilter can be used. The retentatefrom this step is corn oil concentrate while the permeate containingethanol is recycled back for extracting or processed further bydistillation in step 22 or pervaporation in step 25.

If necessary, the filtrate from step 18 can be first passed through anultrafiltration membrane 27 that will restrain the zein and otherco-extracted components that are larger than the oil in molecular size.This ultrafiltration retentate can be further processed to produce zeinas a separate product or be sent to step 19 for desolventizing and thezein recycled back to the ethanol production section. Theultrafiltration permeate now contains oil and ethanol, which can go tothe nanofiltration step 24 as described earlier.

The retentate of the nanofiltration operation in step 24, containingconcentrated oil in ethanol, may then be subjected to evaporation instep 28 to produce corn oil, while the ethanol vapors are recycled tothe ethanol production section.

Depending on the moisture content of the corn and the manner in whichthe plant is operated, the ethanol extractant may absorb water duringthe extraction, filtration, and membrane processing steps. This watermust be removed from the ethanol recycle streams to maintain itseffectiveness for extracting oil. This can be done either bydistillation as, for example, in a separate distillation column or inthe distillation section of the ethanol plant. Water can also be removedfrom the recycle ethanol stream by another membrane technology known aspervaporation in step 25. In any case, the ethanol must be adjusted towithin 90–100% ethanol concentration prior to being used in theextraction step 16.

Referring now to FIG. 2, the process of the invention for a plantprimarily focused on zein production is illustrated. A preferred processsimultaneously concentrates and purifies zein in an ethanol extractusing appropriate membranes. Steps similar to those shown and discussedwith respect to FIG. 1 are labeled with like reference numerals. Thezein extraction preferably begins with whole or raw corn, and subjectedto dry grind step 10 a. For example, a whole ground corn, such as yellowdent #2, may be milled into coarse particles with a hammer mill fittedwith a screen (0.19″, e.g.), and milled into fine powder using a hammermill fitted with a screen (0.025″, e.g.).

The extraction step 16 a uses a lower concentration extractant than thatwhich is used in FIG. 1. The extractant should preferentially extractzein from corn but not oil, though trace amounts of oil and oil-basedcomponents, such as free fatty acids, may be extracted. Ethanolconcentrations in the range of 60–90% ethanol in water have been foundeffective, and a 70% ethanol, 30% water extractant solution ispreferred. It is contemplated that isopropyl alcohol (IPA) could beincluded in the extractant solution in some extraction processes. Forexample, 5% IPA is contemplated, so that a solution of 70 parts of (5%IPA+95% ethanol) to 30 parts water is used. The extractant/watersolution: corn (ground) ratio preferably is between 10:1 and 2:1volume/weight, most preferably 4:1 volume/weight, for example 4 litersof extractant solution to 1 kilogram of ground corn. However, a ratio aslow as 1:1 is also contemplated. The corn and extractant are mixed instep 16 a for extraction of zein. The temperature of extraction shouldbe 25–65° C., (preferably 50° C.) if 60–70% ethanol is used. The time ofextraction should be 10–120 minutes, more preferably between 30 and 60minutes and most preferably 30 minutes if a batch extraction is done.

The extractant solution is obtainable from within the distillationsection of the plant or by adding water to the output of thedistillation step 22 a. The filtration step 18 a will separate othercorn solids for processing, if desired, as discussed above. For example,corn solids may be separated by use of a filter or a centrifugal devicesuch as a decanter. A filter aid such as, but not limited to, celite,may be added in the filtration step 18 a if needed, depending on, forexample, the filtration equipment, the type of filter cloth or paper,etc., and the particle size of the solids being separated. As an exampleof post-separation processing, the separated corn solids from step 18 aare subjected to a desolventizing step 19 a to remove any ethanol thatmay be adsorbed in the corn solids. The ethanol recovered from step 19 ais recycled to the distillation section of the plant, and may be used,for example, for additional extraction and/or diafiltration. Thedesolventized corn solids provide the necessary input for conventionalethanol production.

The filtrate from step 18 a containing oil, ethanol, and co-extractedcomponents such as a small quantity of oil that may be soluble atcertain ethanol concentrations is then processed in a membraneultrafiltration step 26 to restrain zein while allowing ethanol to passthrough. For example, the membranes may be synthetic, semipermeablemembranes. Zein proteins have molecular weights of about 12,000–40,000daltons. Selection of an appropriate membrane with approximate molecularweight cut-offs of 5000 to 20,000 daltons is therefore straightforward.Ultrafiltration membranes that are stable in ethanol, such as those madeby Koch Membrane Systems, Osmonics-Desal, Millipore, Amicon, PCIMembrane Systems, PTI, USFilter, MTR, etc. can be used. It may bedesired to preheat the filtrate or extract from step 18 a before theultrafiltration step 26. The retentate from the ultrafiltration step 26is zein concentrate, while the permeate containing ethanol is recycledback for extraction with make-up ethanol from the distillation sectionof the plant if needed, or processed further by distillation in step 22a or by pervaporation in step 25 a.

Alternatively or additionally, diafiltration may be used in step 26 topurify the zein. For example, fresh solvent (e.g., 70–100% ethanol) maybe added to the zein to wash the zein during ultrafiltration. Theultrafiltration and/or diafiltration step 26 may be repeated severaltimes to further purify and/or concentrate the zein. If diafiltration isrepeated, it may be desirable to add the fresh solvent in stages to theretentate for further purification of the zein. For example, a laterstage of diafiltration may use a higher ethanol concentration (e.g.,80%–100% v/v).

The stream restrained by the membrane filtration step 26 containsconcentrated zein in a 70% ethanol solution (if 70% ethanol/30% waterwas used for extraction and diafiltration). If higher ethanolconcentrations are used in the diafiltration steps, the restrainedstream from the filtration step 26 will contain concentrated zein andhigher ethanol concentrations. After the filtration step 26, alternativesteps can be used to further concentrate and purify the zein. A firstalternative step is evaporation and drying step 28 a. For example,purified zein extract may be concentrated using an evaporator undervacuum, and dried using a spray dryer. The spray drier may have, forexample, an inlet air temperature between 120–125° C., an outlet airtemperature between 70–75° C., and a feed temperature at roomtemperature.

Ethanol-water vapors produced by step 28 a may be sent for recovery bydistillation step 22 a, pervaporation step 25 a or condensed directlyfor use in the extraction step 16 a. A second alternative step is tosend the zein and ethanol stream to a precipitation step 30, where zeinis precipitated out. Adding cold water to reduce the ethanolconcentration below 40% will cause the zein to precipitate out. Afiltration step 32 then produces zein concentrate. Filtrate from thisstep containing ethanol-water is recycled for further extraction,fermentation, or distillation, as discussed above with respect to FIG.1.

The following is a description of several membrane process experiments.This series of experiments illustrates conducting the process in theultrafiltration/concentration and the diafiltration modes.

Materials: Whole ground corn (yellow dent #2) was obtained from aMidwest dry-grind ethanol plant and used without further sieving. Over70% of the particles were 200 microns to 800 microns in size. Ethanol(anhydrous, 200 proof) was obtained from Aaper Alcohol and ChemicalCompany, Shelbyville, Ky. Aqueous solutions of ethanol were prepared ona volume/volume basis. Deionized water was used for all experiments.

Analytical Methods: Total solids (TS) was determined by oven drying at103° C. for six hours. Nitrogen (N) content was determined either by theKjeldahl method or by the Dumas combustion method using a Leco NitrogenAnalyzer model FP 528. Protein is expressed as N×6.25.

Zein Extraction and Filtration: Zein extraction was performed in a batchmode using dry milled corn and 70% aqueous ethanol. The extractionconditions were 50° C., 30 minutes and solvent-to-solids ratio of 4 mlsolvent: 1 gram corn. Upon completion of extraction, corn solids wereseparated from the corn-ethanol slurry by filtering through Whatmanfilter paper #1 (mean pore size rating of 11 microns). The filteredextract was kept at room temperature until analyzed and/or furtherprocessed by ultrafiltration.

Ultrafiltration and Diafiltration. Two membrane devices were used:

(1) A dead-end stirred cell (Amicon model 502) was operated in the batchmode using flat sheets of polymeric membranes with feed volumes of 200ml extract. The cell could withstand pressures up to 75 psi, althoughmost of the experiments were done at 20–40 psi applied with a nitrogengas cylinder. The cell was fitted with a 62 mm membrane disc of area28.7 cm². Membranes were preconditioned as described in, e.g., R. Shuklaand M. Cheryan, Performance of ultrafiltration membranes inethanol-water solutions: Effect of membrane conditioning, Journal ofMembrane Science, Vol. 198, 2002, pages 75–85. The filtered extract (thefeed in the membrane device) was preheated to 50° C., and the cell wascontinuously stirred and kept at this elevated temperature. Permeate wascollected continuously, while retentate samples were collected byreleasing the pressure and taking out an aliquot for protein and totalsolids analyses. For discontinuous diafiltration experiments, freshsolvent (70% ethanol) was added to the retentate in the cell andre-pressurized.

(2) A cross-flow tubular membrane module was operated in the batch modeusing membranes obtained from PCI Membrane Systems, Milford, Ohio with6–10 liters of filtered extract. The PCI membranes were in the form oftubes of 4 feet in length and ½″ in diameter. They were tested in thePCI membrane tube tester, which has six perforated stainless steel tubesinto which the membrane tubes were fitted. Each tube had its ownseparate permeate outlet, allowing the testing of six differentmembranes simultaneously, using the same feed and under the sameoperating conditions. The feed was pumped from a ten-liter feed tankequipped with a heating/cooling coil using an explosion-proof Proconpump (Procon Products, Murfreesboro, Tenn.) to the module. Transmembranepressure (TMP) was measured as the average of inlet and outletpressures, which were measured with pressure transducers (model K1,Ashcroft, Strafford, Conn.). Cross flow rate was measured by an in-linerotameter and set at 15 L/min, equivalent to a velocity of 4 m/s.

A cooling coil was inserted in the feed tank to control temperatureusing cold tap water. Temperature was measured by a bimetal thermometerin the feed tank. The feed tank was sealed with aluminum foil tominimize evaporation. For discontinuous diafiltration experiments, freshsolvent (70% ethanol) was added to the retentate in the feed tank andpumped through the module. Flux is the volume of permeate per unitmembrane area per unit time. It is expressed as liters per square meterper hour (LMH) and is a measure of the capacity of the membrane system.

Results:

AF10 Membrane—The AF10 membrane from PTI, Oxnard, Calif. is made ofpolyvinylidene difluoride (PVDF) and has a low molecular weight cut-off(MWCO) of 5000. However, it gave quite high fluxes (50–60 LMH) at 20 psiand 50° C. with pure aqueous 70% ethanol after conditioning. Filteredcorn extracts were then subjected to several stages of discontinuousdiafiltration. As shown in Table I, the initial volume of 200 ml ofextract was concentrated 4× to 50 ml. Ten ml of the retentate was savedfor analysis. To the remaining 40 ml of retentate was added 40 ml offresh 70% ethanol and concentrated 2×. This means that 40 ml of permeatewas removed in the second stage. This dilution and ultrafiltration wasrepeated for two more stages.

TABLE I Ultrafiltration and diafiltration of corn extract with AF10membrane. The retentate from each stage was diluted with an equal volumeof fresh 70% ethanol and re-ultrafiltered. Data was obtained at 50° C.and TMP of 20 psi. Feed Retentate Permeate Volume Zein Purity Vol. ZeinPurity Vol. Zein Purity Flux Stage (ml) (g/L) (%) (ml) (g/L) (%) (ml)(g/L) (%) (LMH) 1 200 7.3 43 50 20.3 74 150 2.7 29 30 2 80 10.1 74 4020.8 103 40 2.5 36 27 3 60 10.4 103 30 19.3 119 30 2.0 60 25 4 40 9.7119 20 15.3 129 30 3.2 122 22

TABLE II Ultrafiltration and diafiltration of corn extract with U20Tmembrane. The retentate from each stage was diluted with an equal volumeof fresh 70% ethanol and re-ultrafiltered. Data was obtained at 50° C.and TMP of 20 psi. Feed Retentate Permeate Volume Zein Purity Vol. ZeinPurity Vol. Zein Purity Flux Stage (ml) (g/L) (%) (ml) (g/L) (%) (ml)(g/L) (%) (LMH) 1 200 6.6 40 50 11.9 52 150 2.9 22 30 2 80 5.9 52 40 9.753 40 2.7 35 30 3 60 4.9 53 30 6.3 49 30 3.1 60 25 4 40 3.2 49 20 4.7 5720 2.7 79 29 5 20 2.3 57 10 3.9 75 10 2.8 141 20

The zein concentration had increased from 7.3 g/L in the initial feed to15.3 g/L in the final retentate, and the purity had increased from aninitial 43% to >95% in the final retentate (the data show >100% zeinpurity: this is due to errors in nitrogen determinations inherent in theLeco Nitrogen Analyzer as a result of analyzing liquid samplescontaining ethanol). Flux remained high (22–30 LMH).

U20T Membrane: Similar-discontinuous diafiltration experiments wereconducted with the flat sheet U20T membrane (20,000 MWCO) from KochMembrane Systems, Wilmington, Mass. in the Amicon dead-end stirred cell.The corn extract was processed in five stages. As shown in Table II,zein purity had increased from 40% to 75%, but zein concentrationdecreased from 6.6 g/L to 3.9 g/L by the fifth stage. The flux was 20–30LMH. This membrane appears to be too “open” for effective purificationand concentration of zein.

PCI Tubular Membranes: The PCI membrane selected was the ES404 (4000MWCO) made of polyethersulfone. The membrane tube was conditioned to 70%ethanol before beginning the experiments. Flux with the pure 70% ethanolwas 8 LMH at 15 psi and 30° C. Table III shows an experiment with 9.5 Lof corn extract concentrated 5.35-fold by ultrafiltration. Total solidsincreased twofold, while zein concentration increased threefold,resulting in a purity increase from 48% to 73%. However, zein purity didnot appear likely to increase much further with theultrafiltration/concentration mode shown in Table III.

To increase purity further, a diafiltration experiment was conductedwhere fresh solvent is added in stages to the retentate. This is shownin Table IV. The initial corn extract volume was 6 L. After the removalof 3.45 L as permeate, 2 L of fresh 70% ethanol was added, and theultrafiltration repeated. This discontinuous diafiltration cycle wasrepeated two more times. At the end, the final retentate volume was 2.96liters, and the zein concentration remained at about 8 g/L. The zeinpurity had increased from 44% in the initial feed to 97% in the finalretentate.

TABLE III Ultrafiltration of corn extract with PCI 4K MWCO membrane. Theinitial feed was 9.5 liters of extract with TS = 13.06 g/L and 48% zeinpurity. Experiments were performed at 40° C., TMP of 40 psi, andcross-flow velocity of 4 m/s. Feed/Retentate Permeate Volume Total ZeinPurity Vol. Total Zein Purity Flux VCR (L) solids (g/L) (g/L) (%) (L)Solids (g/L) (g/L) (%) (LMH) 1.00 9.50 13.06 6.29 48 — — — — 12 2.247.69 14.24 7.39 52 1.81 9.38 1.61 17 11 1.61 5.89 15.16 8.67 57 3.619.36 1.84 20 8 2.26 4.21 17.64 11.10 63 5.29 9.80 1.90 19 6 4.23 2.2522.42 16.07 72 7.25 10.98 2.00 18 4 5.37 1.77 24.26 17.74 73 7.73 10.842.06 19 2

TABLE IV Diafiltration of corn extract with PCI 4K membrane. The initialfeed was 6 liters of extract with TS = 12.88 g/L and 44% zein purity.The retentate from each stage was diluted with 2L of fresh 70% ethanoland re-ultrafiltered. Experiments were performed at 40° C., TMP of 40psi and cross-flow velocity of 4 m/s. Feed Retentate Permeate VolumeZein Purity Vol. Zein Purity Vol. Zein Purity Flux Stage (L) (g/L) (%)(L) (g/L) (%) (L) (g/L) (%) (LMH) 1 6.00 5.73 44 2.55 8.92 56 3.45 1.7617 9.2 2 4.55 6.34 56 2.61 8.60 66 1.94 1.77 23 3.1 3 4.61 4.87 66 2.868.21 82 1.75 1.61 36 2.5 4 4.86 5.60 82 2.96 7.57 97 1.90 2.7 40 2.1

The final retentate shown in Table IV was diafiltered with another fivevolumes of fresh 70% ethanol, but the zein purity of the dried retentatedid not increase further, indicating that the optimum level ofdiafiltration is probably between three and four stages for theconditions shown in Table IV. As shown, ultrafiltration anddiafiltration can thus result in zein purities of greater than 90%.

FIG. 3 shows the process of the invention applied to a plant forproduction of both oil and zein, as well as ethanol and DDGS. The firstextraction step 16 b and first filtration step 18 b are the same as inFIG. 1, with a 90–100% ethanol concentration used for oil extraction.The filtrate from 18 b is subjected to a nanofiltration step 24 b toproduce an oil concentrate as described earlier for FIG. 1. Zeinextraction is small, especially when concentrations of ethanol approachabout 95% ethanol or more. If an amount of zein is significant, then anultrafiltration step 27 b could be conducted before step 24 b asdescribed earlier for FIG. 1.

The corn solids from 18 b are extracted again in step 34 with a lowconcentration of ethanol in the range of 60–90%, preferably 70%ethanol/30% water as described for FIG. 2. Zein and ethanol-waterobtained from a second filtration step 36 are processed byultrafiltration step 26 b and combined with any zein-alcohol retentatefrom the ultrafiltration step 27 b. The permeate from step 26 b isethanol-water which proceeds as described for FIG. 2. In addition, thezein concentrate can be processed as described with regard to FIG. 2 toproduce zein.

The invention therefore provides efficient, flexible and simpleprocesses for production of corn products. The same production line maybe used to maximize oil production or zein production. Zein and oilproduction may also be conducted in parallel fashion. Because theinvention may process dry corn, as well as wet milled corn product, itprovides the ability to achieve corn product production from dry millplants used currently for ethanol production only. Reagent forextraction use in the extraction step(s) of the invention is regeneratedor produced within the plant itself. Individual equipment componentsapplied in the processes are modular and conventional, thus allowingstraightforward modification of existing plants as well as constructionof new plants.

While various embodiments of the present invention have been shown anddescribed, it should be understood that other modifications,substitutions and alternatives are apparent to one of ordinary skill inthe art. Such modifications, substitutions, and alternatives can be madewithout departing from the spirit and scope of the invention, whichshould be determined from the appended claims.

Various features of the invention are set forth in the appended claims.

1. A process for removing oil from an agricultural substrate, includinga dry grind corn, the process comprising: mixing an ethanol solutioncomprising ethanol and water with a concentration in the range of fromabout 90% to about 100% ethanol with the dry grind corn in a ratio offrom about 10:1 to about 1:1 to form an extraction solution includingthe ethanol solution, oil, and corn solids; separating the extractionsolution into the corn solids and a filtrate, the filtrate including theethanol solution and oil; membrane filtering the filtrate to restrain anoil concentrate from the filtrate and passing a permeate of the ethanolsolution, said membrane filtering including nanofiltration; and,purifying the oil contained within the oil concentrate.
 2. The processof claim 1 wherein the step of membrane filtering the filtrate includespassing the filtrate through a nanofiltration membrane with a molecularweight cut-off such that particles having a molecular weight in therange of from about 800 daltons to about 900 daltons are restrained. 3.The process of claim 1 wherein the step of purifying the oil containedwithin the oil concentrate includes evaporation of the ethanol solution.4. The process of claim 3, further comprising: recycling ethanol fromsaid evaporation.
 5. The process of claim 1 wherein the step of mixingthe ethanol solution and the dry grind corn is performed at atemperature in the range of from about 60° C. to about 90° C.
 6. Theprocess of claim 1 wherein the step of mixing the ethanol solution andthe dry grind corn is performed for a period of time in the range offrom about 10 minutes to about 120 minutes.
 7. The process of claim 1wherein the ethanol solution includes ethanol, water and isopropylalcohol.
 8. The process of claim 1 wherein the step of membranefiltering further comprises diafiltering.
 9. The process of claim 1,wherein the corn comprises whole, raw corn.
 10. The process of claim 1,further comprising, before said extracting, dry grinding the whole, rawcorn.
 11. The process of claim 1 wherein said extracting comprisesextracting from dry milled corn.
 12. The process of claim 1, wherein thecorn is not wet milled before said extracting.
 13. The process of claim1, further comprising: processing the permeate including ethanol toprovide recycled ethanol.
 14. The process of claim 13, wherein saidprocessing the permeate comprises distillation.
 15. The process of claim13, wherein said processing the permeate comprises pervaporation.